overboost. help welcome

[ragingfool]

hi all
finally solved my code 26 problem last month.
seems someone rearanged the relays forward and
aft. I had to ohm out the wires from the ECU
to find the problem. Doh!

anyway, back then i installed a new boost control
frequency valve. the trouble now is anytime i get
the pedal near the floor, the boost pressure goes
past 1 bar and the ECU cuts the spark and fuel.
i did a leakdown test on the wastegate plumbing.
there was a slow leak (1 bar to 0 in about 3 min)
wastegate adjustment is correct. i even adjusted
the wastegate so that max boost was about 4 psi
with the frequency valve connector off, but with
the connector on, still got overboost.
it seems that the valve is venting the wastegate
too fast.
i have the S4 memcal
thanks for any help

chris
90SE

[Paula&Marcus]

Chris,
set your mechanical boost prerssure to 0.65 bar (around 9-10 psi) not less !

Marcus

[ragingfool]

[quote=Paula&Marcus]Chris,
set your mechanical boost prerssure to 0.65 bar (around 9-10 psi) not less !

Marcus[/quote]

naturally I did set it back.
either way i get crazy overboost.
any ideas?

thanks

[Paula&Marcus]

ragingfool said:

[quote=Paula&Marcus]Chris, set your mechanical boost prerssure to 0.65 bar (around 9-10 psi) not less ! Marcus

naturally I did set it back.
either way i get crazy overboost.
any ideas?

thanks[/quote]

Chris,
Make a test ! Remove the electrical connector from your solenoid valve. If you like to avoid code 26 + CEL light to come on, just insert a 47 Ohm resistor into the connector. (This will fool the ECU = still believes that there is the solenoid connected).
When you go on a test run you should see max. 0.65-0.7 bar rock solid, not more, not less.

Please report.

Marcus

[ragingfool]

Marcus,
with frequency valve connector off
i get steady 9.5 psi @WOT. (mechanical boost guage)
sorry, thought i reported that.
seems the "open" pulses are too
wide and/or not modulated by the ECU
like they should be, or the feedback
loop is too slow.
what are the conditions for determining
pulse width? does the ECU start out
wide then go to narrow as pressure rises?
thanks

[arium]

What are your map readings at. Bad map sensor or that thin little plastic line going to it off of plugged maybe. I believe the manual has a chart for different output voltage versus pressure. Go through the whole range to make sure the thing is registering linear values through its whole range.

Just a thought as it would be the sensor determining the pulse width for boost control.

Steve

[ragingfool]

arium said:

What are your map readings at. Bad map sensor or that thin little plastic line going to it off of plugged maybe. I believe the manual has a chart for different output voltage versus pressure. Go through the whole range to make sure the thing is registering linear values through its whole range. Just a thought as it would be the sensor determining the pulse width for boost control. Steve

MAP on Freescan is 2.2 when I hit 15 psi on guage, TPS at 58% and thats spot on. i cant get the throttle near the floor unless i'm in a high gear going really fast and start SLOWLY easing the pedal down.
MAP is near 0 on Freescan at 0 TPS.
wastegate frequency valve duty cycle started dropping as MAP went above 1.5 but too slow.
freescan was on 100ms sample and MAP went from 1.3 to 2.2 in .6sec (so did mech boost guage)
sent log to Dermot to check out
thanks for the help, I appreciate it
chris
90SE